Electronic circuits typically require voltage or current references in order to operate effectively. Voltage references may be required that are temperature independent. This may be useful in circuits that require a fixed voltage reference. Voltage reference may also be required that are temperature dependent. Such references may be used as temperature sensors. One circuit arrangement commonly used to provide a temperature dependent voltage reference utilises a pair of bipolar junction transistors (BJTs). It is possible to generate a voltage reference that is proportional to absolute temperature (PTAT) by using two BJTs with different collector current densities. The difference in the base-emitter voltages of each BJT can be reflected across a resistor in order to produce a PTAT voltage reference. By combining a PTAT voltage reference with a complimentary to absolute temperature (CTAT) component a voltage reference that is independent of temperature may be provided.
A problem with BJT-based voltage references is that the output is affected by the BJT current gain factor. This is particularly the case in some types of processing, such as CMOS, where BJTs have a low current gain factor. There is therefore a need for voltage reference circuits in which the output voltage reference is not affected by the BJT base currents.